The invention relates to a minimal-amount powder metering device, in particular for pharmaceutical or chemical applications for metering powder volumes of less than 1 cm3, preferably less than 150 mm3, comprising a metering chamber which is delimited by a surrounding wall and which can be connected to a vacuum source for suctioning powder in order to fill the metering chamber with powder to be metered, filtering means for retaining powder in the metering chamber (and thus preventing powder from being sucked into the vacuum source) during a suctioning process, i.e. during filling, being associated with the metering chamber. The surrounding wall delimits the metering chamber preferably in the outward radial direction, in particular in relation to a preferably vertical metering-chamber axis which preferably extends perpendicular to a metering-chamber filling and/or emptying opening and/or coincides with a displacement axis (to be explained later) of a preferably provided ejection plunger.
Furthermore, the invention relates to a method for metering minimal amounts, in particular having a mean particle diameter of x50.3<50 μm. The powders preferably are pharmaceutical or chemical substances. In a particularly preferred manner, the method is carried out using a minimal-amount metering device according to the invention. The method also requires a metering chamber for powder to be metered, the metering chamber being filled with powder to be metered by applying a vacuum to the metering chamber, the vacuum being applied through filter means so as to retain most of the powder suctioned during a metering process in the metering chamber by means of said filtering means.
From EP 2 652 451 B1, a powder metering device is known in which a metering chamber delimited by a surrounding wall is filled with powder to be metered by applying a vacuum to the metering chamber through a filter membrane. Said known powder metering device is very advanced compared to other powder metering devices known before because the metering chamber is filled and emptied through one and the same opening, whereas in older metering devices, the powder to be metered was sucked in through a lateral filling opening and discharged downward by applying pressure.
The known technology reaches its limits with minimal amounts or minimal volumes of powder because as the metering-chamber volume decreases, the available filter surface theoretically decreases as well until typically screen-shaped filter membranes that small can barely or no longer be fabricated. Moreover, the porosity, i.e. the maximum possible flow through such a small filter membrane decreases to very small values at which the transfer of gas, i.e. a suctioning of gas through the filter membrane becomes highly problematic and thus a secure, in particular complete filling of the metering chamber can no longer be ensured. Moreover, very small filter membranes such as the ones that would be needed for the minimal amounts of interest here would be extremely fragile and difficult to seal.
Solutions are sought to overcome the aforementioned problems, in particular in view of growing efforts to achieve individualized metering of active pharmaceutical ingredients (API) of drugs. The current practice of large-scale metering consists in the active ingredient first being mixed with an excipient and then metering them together in larger metering volumes. However, the problem here is the relatively non-homogenous mixture and the lack of an option of individualized, i.e. patient-specific metering. Hence, a metering device and a metering method are to be provided that meet these requirements and allow minimal amounts (of active ingredients) to be metered accordingly and preferably be added to an excipient.